CHEMISTRY. 269 



as fuel, the advantages of which are the ease with which it 

 can be regulated, the completeness of its combustion, the 

 readiness with which cleanliness can be maintained, the high 

 heating power of such material, etc. The requirements of 

 such a gas are, 1st, it should consist of combustible constitu- 

 ents only; 2d, it should be possessed of high heating power; 

 and, 3d, it should produce on burning compounds of low spe- 

 cific heat. Hitherto coal-gas has been the only gas avail- 

 able for heating, and, notwithstanding the disadvantages at- 

 tending its use, has proved itself a cheaper, more effective, 

 and more easily managed fuel than coal, wood, or other 

 forms of solid heat-giving material. Latterly, however, the 

 so-called water-gas, produced by passing superheated steam 

 over anthracite coal at full redness, has come forward with 

 much promise, improved machinery of preparation allowing 

 it to be easily and cheaply produced on the large scale. 

 Though the heating power of water-gas is only about one 

 fifth of that of ordinary coal-gas, yet the cost of the gas is 

 so much less that an actual saving of from one third to two 

 thirds is effected by its use. By the use of oxygen in the 

 blast a gas of very high heating power might be produced. 



Long has made a series of experiments on the decomposi- 

 tion of steam by ignited charcoal for the production of water- 

 gas. In his earlier experiments the results were complicated 

 by the evolution of absorbed gases from the charcoal. When 

 this source of error was allow r ed for, it was observed that no 

 fixed relation existed between the carbonous oxide and the 

 carbon dioxide present. But the author noticed that the 

 carbonous oxide was directly as the amount of charcoal pres- 

 ent in the tube. Hence it is evident that hvdro^en and car- 

 bon dioxide are at first formed, and then that the latter gas 

 is reduced by the excess of ignited carbon. If, however, 

 there be an excess of steam present, this is reduced, and car- 

 bon dioxide again formed. 



Professor Church makes the curious observation that the 

 deterioration of the leather binding of library books, which 

 is often rendered quite friable in time, is brought about by 

 the action of the sulphurous gases given off in the burning 

 of common coal-iras. He has noticed that it is the books on 

 the uppermost shelves of the libraries that are the most af- 

 fected a fact which, as the combustion products in gradu- 



